A thermal system is used to elevate the temperature of exhaust gas to activate a selective catalytic reduction (SCR) catalyst in a vehicle exhaust system. The SCR catalyst reduces levels of NOx using ammonia as a reductant. The reducing agent, such as diesel exhaust fluid (DEF) for example, reacts with NOx to convert pollutants into nitrogen and water. The catalyst is arranged in a housing having an outlet to a tailpipe. The tailpipe is subject to a temperature limit to avoid overheating the ground/road. When there are tight packaging constraints it is challenging to effectively control a tailpipe outlet temperature from the housing. It is therefore desirable to provide a thermal management system that can control outlet temperatures.